Question

Describe the process of DNA replication

Answer 1

Answer :- DNA replication is the duplication process by which a DNA molecule produces exact copies of its own structure.

The process of DNA replication is divided into 3 steps i.e initiation , elongation and termination which described below......

•Initiation phase :-

i. In the start of this phase the two antiparralel strands of a DNA started to unwind at a specific region of starnds , this region is known as origin of replication.

ii. In the origin of replication the DNA unwinding protein is added . This unwinding protein is known as helicase which help to break the hydrogen bond between the two strands of DNA.

iii. After that at the origin of replication Y shaped replication fork is formed. Then the single stranded binding protein or SSBp are added at the two separated strands of DNA which help to prevent the DNA strands to form hairpin like structure.

iv. In the next step of initiation DNA gyrase enzymes are added at the DNA strands which help to separate the super coiling region of DNA.

v. Then in the next step RNA primer are added at the replication fork. This RNA primer is synthesized by RNA polymerase enzyme close to origin of replication.

vi. Then synthesis of new DNA strand take place by the addition of DNA nucleotides to the ribonucleotide of the RNA primer. This leads to the elongation of the primer nucleotide in the 5'-3' direction. This is catalysed by enzyme DNA polymerase.

• Elongation phase :-

i. After the addition of primer the at the free 3' -OH region of primer nucleotides are added one by one by DNA polymerase III enzyme and this addition of nucleotides are goes on towards 5'-3' direction.

ii. On one parent DNA strand , the daughter strand is synthesized as a continuous strand. This strand is called leading strand because it is synthesized first.

iii. On the second DNA strand , the daughter strand synthesis begins slightly later. Hence this daughter strand is called lagging strand. The lagging strand is synthesized in short fragments called Okazaki fragments. This replication is discontinuous because the DNA is synthesized in short fragments.

iv. Each Okazaki fragments starts with an RNA primer. Later the RNA primers are removed by DNA polymerase I enzyme.

v. Then the DNA ligase enzyme joins the Okazaki fragments into a long polynucleotide chain.

•Termination phase :-

This replication process is terminated when the strands reach the opposite region of origin of replication which is known as termination region where different genes are there e.g tus gene. This genes are actually stop the movement of replication fork.

So from the above discussion we are come to know the actual process of DNA replication.